Decreased human mobility during the COVID-19 pandemic may have affected North American birds' activity, according to a new study. Two research teams from the University of Manitoba and the Cornell Lab of Ornithology examined records of around 4.3 million birds between the months of March and May in the years 2017 through 2020.
The results were overwhelming. During the pandemic, 80% of the 82 species studied were found in significantly greater numbers closer to human-inhabited areas, including within 62 miles of cities, major highways and airports, as compared to pre-pandemic levels.
"A lot of species we really care about became more abundant in human landscapes during the pandemic," Nicola Koper of the University of Manitoba said. "I was blown away by how many species were affected by decreased traffic and activity during lockdowns."
Bald eagle sightings increased in cities with the strongest lockdowns, and red-throated hummingbirds were three times as likely to be within two-thirds of a mile of an airport.
The researchers noted that since their data relied on volunteer sightings, it was possible that the increase in numbers could be because there were simply more people birdwatching during the pandemic.
"Were species being reported in higher numbers because people could finally hear the birds without all the traffic noise, or was there a real ecological change in the numbers of birds present?" co-author Alison Johnston from the Cornell Lab of Ornithology asked.
However, if that were the case, the scientists said they'd expect more sightings of bigger birds — which are easier for amateur birdwatchers to spot — and fewer sightings of smaller birds like hummingbirds and swallows. But that wasn't the case. The effects of lockdowns were noted across 66 of the 82 species, and species were 14 times more likely to be seen during the pandemic.
Interestingly, sightings of some species decreased due to the lack of human movement, according to the study. Red-tailed hawks, among others, were seen much less than in previous years. Researchers believe this may be because traffic declined during the pandemic, and as a result there was less roadkill.
The authors noted that the long-term effects of the behavioral changes remained unclear, and they encouraged future studies to look at birds' life span, nest success and population sizes post-pandemic.
"The widespread increases in counts of birds in response to reduced human activity during the pandemic suggest that a sustained reduction of vehicular traffic and human activity might have lasting benefits to birds," the study concluded.
The researchers applauded volunteers who helped them accrue the massive amounts of data.
"Having so many people in North America and around the world paying attention to nature has been crucial to understanding how wildlife react to our presence," lead author Michael Schrimpf, from the University of Manitoba, said.